Comparison of techniques for the isolation of sediment pore water for toxicity testing

Abstract

The objective of this study was to define an interstitial (pore) water isolation technique suitable for sediment toxicity testing and toxicity identification evaluation (TIE) research. Pore water was prepared from sediments collected at two fresh-water sites (Saginaw River, Keweenaw Waterway) using four or five different techniques, and the samples were compared with respect to toxicity to Ceriodaphnia dubia and several inorganic chemical parameters. Methods evaluated were: high speed (10,000×g) and low speed (2,500×g) centrifugation, syringe extraction, compression, and dialysis. Both high speed and low speed centrifugation resulted in adequate volumes of pore water for routine testing with relatively minimal effort, while the other three techniques were labor intensive and/or yielded small quantities of pore water. Filtration of samples either during preparation (syringe-extraction, compression) or subsequent to initial isolation (centrifuged samples) resulted in significant losses of toxicity, apparently due to the adsorption of contaminants onto the filter or particles retained by the filter. Low speed centrifugation generally resulted in much higher metal concentrations than the other four techniques. However, compared to samples prepared by high speed centrifugation or dialysis, a relatively high proportion of the metals in pore water isolated by low speed centrifugation were biologically unavailable, as inferred from the results of the toxicity tests. Based on these studies, as well as the work of others, we recommend that sediment pore water for toxicity testing and/or TIE analyses be prepared by centrifugation (preferably at 10,000×g) without subsequent filtration.